Method for purifying fresh, combined and saline wastewater from radioactive heavy metals

ABSTRACT

The invention relates to environment management, particularly to methods for purifying a wastewater in order to climate a toxic impact of heavy and radioactive metals. A method for purifying fresh, combined and saline wastewater from radioactive and heavy metals using an electrolysis and a special active substance (sorbent), wherein the wastewater is fed to an electrolyzer with a chamber that is separated by a special membrane that is permeable for ions of metals separately of water, then changes of the pH occur in order to form complex compounds, which comprise ions of radioactive and heavy metals. Afterwards, the adsorption of the obtained compounds by the special active substance (sorbent) and filtering-off on a precoat filter that retains ions of heavy and radioactive metals are performed. The obtained filtrate is cemented without drying and evaporation in order to perform final deposition of the radioactive compounds.

The invention relates to environment management, particularly to methods for purifying a wastewater in order to eliminate a toxic impact of heavy and radioactive metals.

“A METHOD FOR PURIFYING WATER FROM RADIOACTIVE CONTAMINATIONS” is known, wherein the purification is performed by filtration through a sorbent—aluminum oxide. A mixture of aluminum oxide and 30-50 wt. % of anionite-inertone relative to the total amount of the mixture is used as the sorbent, wherein the sorbent is arranged between two porous titanium partitions, which are located at a distance of 10-15 mm between each other (Ukrainian patent No. 2349 as of Jan. 31, 1994).

A drawback of the known method lies in a low efficacy of water purification from radioactive contaminations, also the method allows to purify fresh water only.

The closest one to the claimed invention is: “A method for purifying liquid radioactive wastes and wastewater”. The method for purifying liquid radioactive wastes and wastewater is implemented by means of introducing a sorbent into a solution, the method is characterized in that the natural organogenic sorbent is put into an ion-penetrating shell having a coaxially arranged electrode (cathode) and an external opposite electrode (anode), the shell is put into the solution to be purified, a potential is applied between the electrodes, which acts to cause a directed movement of cations from the solution to be purified to the sorbent followed by their retention in the sorbent matrix (Ukrainian patent No. 78704 as of Apr. 25, 2007).

Drawbacks of the method lie in that the proposed method is used to purify fresh water only.

A problem to be solved by the present invention is to develop an effective method for purifying fresh, combined and saline wastewater from radioactive and heavy metals by means of binding ions of radioactive and heavy metals into stable complex compounds. With further filtration of the contaminated water and stable complex compounds on a precoat filter with an active substance (sorbent).

The stated problem is solved as follows.

In the method for purifying fresh, combined and saline wastewater from radioactive and heavy metals using electrolysis and active substance (sorbent), according to the invention, the wastewater is fed to an electrolyzer with a chamber that is separated by a membrane that has low throughput capacity for water, but is permeable for ions of metals. A direct current is supplied to the electrodes of the electrolyzer. The water electrolysis occurs until lowering the water pH in one chamber and increasing the water pH in another chamber. Then, the wastewater from both chambers is mixed and fed to a retention basin until forming complex compounds, which comprise ions of radioactive and heavy metals, are adsorbed by the amulinum-, titanium- and oxygen-based active substance (sorbent) with addition of the hydrogen peroxide, are filtered-off on a precoat filter that retains ions of heavy and radioactive metals in the bound form of complex compounds. The obtained filtrate is cemented without drying and evaporation in order to perform final deposition of the radioactive compounds. Kieselgur and amulinum-, titanium- and oxygen-based active substance (sorbent) are used as a filtration membrane on the precoat filter.

The method is performed as follows.

The contaminated wastewater is fed to the electrolyzer with chambers, which are separated between each other by the membrane that has low throughput water capacity, but is permeable for ions of metals. The direct current with voltage of from 5 to 220 volt and amperage of from 0.1 to 10 ampere per cm² of interelectrode area is supplied to the electrodes, which are made of titanium or titanium-aluminum alloy. The contaminated wastewater is retained in the electrolyzer until lowering of the water pH <2 in one chamber and increasing the water pH in another chamber for up to >12. The change of pH in the water occurs due to accumulation of OH ions in the course of the water electrolysis. The ratio between the volume of the electrolyzer chambers lies within the range of from 1:1 to 3:1. Then, the contaminated wastewater from both chambers is mixed and fed to the retention basin. The contaminated water is retained in the retention basin for 1 hour, where ions of radioactive and heavy metals are bound into stable complex compounds, which are formed with titanium or aluminum. The complex compounds of radioactive, heavy metals and titanium or aluminum are adsorbed by means of addition of a suspension of the active substance (sorbent) in the amount of 1-50 mg/l and 50% of the hydrogen peroxide in the amount of 0.3-20 mg/l to the water. After addition of the active substance (sorbent) and of the hydrogen peroxide, the water is retained in the retention basin for 12-48 hours under the temperature of from 20° C. to 70° C. Afterwards, the contaminated water with a residue is fed to the precoat filter for filtration. Wherein kieselgur and the active substance (sorbent) are used as a precoat membrane on the filter. Ions of heavy and radioactive metals are retained in the bound form of the complex compounds and are retained by the filter material. The filtrate obtained from the filter is cemented in order to perform final deposition of the radioactive substances.

The claimed method provides for purification of water of ions from heavy and radioactive metals, which are retained in the bound form of the complex compounds that significantly reduces their movability during the period of the long-term final deposition of the radioactive substance. Furthermore, this method allows performing purification of water from radioactive and heavy metals having different salinity (from fresh one to sea one). 

The invention claimed is:
 1. A method for purifying wastewater comprising radioactive heavy metals using electrolysis and a sorbent that is based upon at least one of aluminum, titanium and oxygen, the method comprising: (a) Feeding the wastewater to an electrolyzer having a membrane that separates the electrolyzer into a first chamber and a second chamber, the membrane having a limited throughput capacity for water but permeable for ions of metals; (b) Supplying a direct current to the electrolyzer having electrodes so that water electrolysis lowers the wastewater pH in a first chamber and increases the wastewater pH in a second chamber, then; (c) Mixing the wastewater from the first chamber and the second chamber, then; (d) Feeding the mixed wastewater to a retention basin, the mixed wastewater therein forming complex compounds which comprise ions of the radioactive heavy metals, and wherein the radioactive heavy metals are adsorbed by the sorbent with addition of hydrogen peroxide, and then; (e) Filtering off the complex compounds on a precoat filter that retains the ions of the radioactive heavy metals in a bound form of the complex compounds.
 2. The method for purifying wastewater according to claim 1, characterized in that kieselgur and the sorbent are used as a filtration membrane on the precoat filter.
 3. The method for purifying wastewater according to claim 1, wherein the wastewater comprises fresh water.
 4. The method for purifying wastewater according to claim 1, wherein the wastewater comprises saline water. 